Callithrix jacchus infants are raised in complex family environments with all members helping to rear the young. Due to the high birth weight of twin infants, high fecundity of females and need to carry the infants throughout the day, fathers and siblings are needed to raise infants successfully. Previous studies examining male parental behavior have focused on infant carrying with observations made within the family context. This study developed a method to examine a male’s interest in infants when released from family influences and to determine the natural variation in paternal expression. Ten experienced common marmoset fathers were evaluated using three different measures of parental behavior: 1) Focal animal sampling was recorded in family groups for two weeks postpartum; 2) Five daily instantaneous scan samples monitored carry behavior in families; and 3) Then fathers were tested alone in a specially designed cage in a separate room using a crossover design with four stimuli: familiar infant, unfamiliar infant, familiar vocalization and unfamiliar vocalization. Males showed 40-fold inter-individual variation in expression of parental care. Fathers who showed little involvement in infant care in the home cage could express a high level of motivation to respond to infant stimuli in the testing cage. There was no significant correlation between measurements of paternal care in the family context versus responsiveness scores to infants outside (Spearman r2= 0.008). The lack of correlation illustrates that the presence of other family members affects expression of paternal behavior. Grant MH070423.